Impacts of traditional livestock corrals on woody plant communities in an East African savanna

In African savannas, humans and their livestock leave long-term legacies on the landscape in the form of abandoned livestock bomas (corrals). Once abandoned, bomas develop into nutrient-rich herbivore hotspots characterised by distinctive plant communities. Impacts of bomas, however, extend beyond the boundaries of the boma site itself. This is especially true for woody species which are intensively harvested for boma fencing material and fuel wood. Following boma abandonment, it is not clear how quickly, or to what extent, woody plant communities may change and develop over time. A chronosequence approach was used to investigate the effects of traditional livestock bomas on woody plant communities over time in an Acacia drepanolobium Sjost. savanna in central Kenya. Densities of woody species associated with boma sites that had been abandoned <4, 7-42, and >42 years before were measured. Reductions in densities of the dominant tree, A. drepanolobium, were still detectable after >42 years, especially in the highest impact zones at boma edges (up to 60 m from the boma). Despite these overall reductions, the edge zones of old boma sites had unusually high densities of very large A. drepanolobium trees. Woody species richness increased at edges of newly abandoned bomas, as did densities of the uncommon shrub Lycium europaeum L., and these changes persisted for several decades. These patterns likely result from interactions among species within the woody plant community, as well as interactions with herbivores and edaphic factors.